Reciprocating hermetic compressors consist of a motor-compressor assembly mounted in the interior of a hermetically sealed shell generally by suspension springs. The motor-compressor assembly comprises a cylinder block sustaining a vertical crankshaft carrying, medianly, a rotor of the electric motor of the compressor and, inferiorly, a pump rotor which conducts, during the operation of the compressor, lubricant oil from a reservoir provided in a lower portion of the shell of the compressor to the parts with relative movement, in order to form an oil film between said parts, avoiding the wearing contact therebetween.
These compressors present a connecting rod mounted, at one end, to an eccentric of the crankshaft and, at the other end, to a piston reciprocating in the interior of a cylinder orthogonally in relation to the axis of the eccentric between a lower dead point condition and an upper dead point condition, which are respectively defined by a maximum and a minimum linear spacing between the piston top and a valve plate mounted to a cylinder end and which defines the internal face of a cylinder head assembly defining suction and discharge chambers of the compressor.
When driven by the electric motor, the piston is reciprocally displaced inside the cylinder, drawing and compressing the refrigerant gas.
The hermetic shell further carries a discharge duct or tube presenting an internal end affixed to the cylinder head and opened to the discharge chamber, and an opposite end opened to an orifice provided on the surface of the hermetic shell, communicating the discharge chamber with the high pressure side of a refrigerating system to which the compressor is connected.
When an insulation failure occurs in the motor of a compressor, there occurs leakage of electric current, which has two paths to follow: through the suspension springs or through the discharge tube.
The current leakage mostly occurs in three possible situations: the refrigeration appliance to which the compressor is associated is not grounded and the user experiences electric shocks with life risks; said refrigeration appliance is grounded and a moderated current passes through the grounding system, causing degradation of the electrodes and increasing energy consumption; and said refrigeration appliance is grounded and a high current passes through the system without being detected by the thermal protector, jeopardizing the installation.
Nowadays it is usual the provision of insulating stop means, such as plastic stop means, in the suspension springs, aiming at reducing the passage of noise. Besides the function to which they are intended, such stop means also actuate as electric insulators, preventing the passage of electric current to the shell of the compressor. In such constructions, insulation failures generate electric current leakage through the discharge tube.